Igneous Rocks/Processes

Igneous Rocks/Processes

1. Volcanoes

   • Cinder cone: explosive only, small
   • Composite volcano- explosions and eruptions, lava flows and landslides, light ash fall, felsic to intermediate
   • Shield- wide and a hotspot
   • Caldera- explosive, begins to reform after cone blown off, volcano collapses into magma chamber, huge hole- eventually a lake
   • Supervolcano- under yellowstone, huge, deep magma chamber, if erupts- could wipe a continent
   • flood volcanism- fissure related, mafic and basaltic
   • hotspot volcanism- intraplate, volcanoes inside plates

2. Magma

   • Cooling
     • plutonic rocks- crystallized magma at depth, big crystals
     • volcanic rocks- crystallized lava at surface, small crystals
     • volcanic glass- very fast cooling lava at surface, no crystals
   • Types
     • Felsic- light colored, high silica %
     • Intermediate- medium colored
     • Mafic- dark gray to black, increased magnesium and iron %
     • Ultramafic- very dark green to black, extremely high % of magnesium and iron

3. Extrusive rocks

   • Secondary
     • lahars- when water, molten material, and ash meet = like a mudflow
     • ash fall- inches to feet
   • Explosive
     • pyroclastic flow- ash and molten rock explode, create a dense, fast cloud thats almost solid
     • bombs- fragments of volcano or molten rock that fly through the air
   • Effusive
     • lava flows- ropey (pahoehoe) or gravelly (aa) texture, speed and texture depends on chem composition, mafic and basaltic have few explosions, felsic- hella explosions
   • Fissure
     • dikes reach surface and erupt, lava flows

4. Intrusive rocks

   • rocks that form when magma intrudes into other rocks
   • dike- near vertical intrusion, sheet-like magma, ex: New Mexico dike
   • sill- near horizontal intrusion, sheet-like magma
   • batholith- very large igneous intrusions that go very deep into the earth's crust; the sierra nevada
   • laccolith- sheet intrusion that has been injected between 2 layers of sedimentary rock

5. How other rock types happen

   • mafic forms first, taking up iron and magnesium
     • intermediate begins to form
       • magma cooling, felsic begins to form
         • magma extremely cool due to increased silica %